A polyether ester block copolymer consists of a hard segment and a soft segment. Mainly, polybutyleneterephthalate is used as a hard segment and polyoxyalkylene glycol ester is used as a soft segment. A polyether ester block copolymer can be produced by copolymerizing the hard segment and the soft segment. This copolymer is a substance which has characteristics of both engineering plastic (durability, heat resistance, oil resistance, chemical resistance, ozone resistance, molding processability, etc.) and rubber elastic body (sound deadening quality, impact resistance, repulsion resilience, low-temperature resistance, bending-fatigue etc.) and is widely used, for example, as auto parts, industrial parts, precision machine parts, electric/electronic device parts, fiber, film and articles of daily use. In particular, application as a structural member of auto parts, industrial parts, precision machine parts and electric/electronic device parts has been actively pursued.
Generally, polyoxytetramethylene glycol (hereinafter abbreviated as “PTMG”, as appropriate) has been widely used as polyoxyalkylene glycol to be used for a polyether ester block copolymer. However, its elasticity, heat resistance and low-temperature resistance are not always satisfactory. In order to overcome these difficulties, a polyether ester block copolymer using polyoxytetramethylene glycol ester as a soft segment, which was selected from among various combinations of each segment, has been proposed and claimed to be excellent in elastic recovery, a property of returning to original state as an elastic body when, for example, stretched (refer to Patent Document 1).
Further, in order to overcome the above difficulties, a polyether ester block copolymer has been proposed using polybutylene terephthalate as a hard segment and polyoxytrimethylene glycol ester as a soft segment and whose weight ratio of the soft segment is 60 to 90%. The above-mentioned elastic recovery of this copolymer has been disclosed to be the most excellent (refer to Patent Document 2).    [Patent Document 1] Japanese Patent No. 3164168    [Patent Document 2] U.S. Pat. No. 6,562,457